MAX phase-based materials for the MYRRHA pump impeller

Thomas Lapauw, Konstantza Lambrinou

    Research output


    The heavy liquid metal (HLM) coolants (Pb, LBE) used in Gen-IV lead fast reactors (LFRs) tend to corrode the structural candidate steels, due to the significant solubility of certain steel alloying elements (Fe, Ni/Mn, Cr) in the HLM at elevated temperatures. The HLM used in the MYRRHA nuclear system as both coolant and spallation target is the liquid lead-bismuth eutectic (LBE). Since fast-flowing LBE tends to erode severely the steel components with which it comes into contact, it is necessary to identify more durable material alternatives for the construction of the pump impeller of the MYRRHA system. The MYRRHA pump impeller is called to operate at 300°C in contact with fast flowing LBE: preliminary estimations have shown that the LBE flow velocity is expected to reach locally 10 m/s on the pump impeller surface. Amongst the considered material alternatives that could potentially meet the material requirements imposed by this application are MAX phases and composites thereof.

    MAX phases are ternary carbide and nitride compounds described by the general formula Mn+1AXn, where n = 1, 2, or 3. In the periodic table of elements, M is an early transition metal, A is an A-group element (usually, IIIA and IVA), and X is carbon (C) or nitrogen (N). Depending on the number of M, A and X atoms in the compound, the so-far identified MAX phases are divided into three groups: the 211, 312, and 413 materials [1]. What makes the MAX phases interesting materials with great application potential is their remarkable combination of chemical, physical, electrical, and mechanical properties, some of which are characteristic of metals and some of ceramics. For example, MAX phases are typically resistant to oxidation and corrosion, refractory, light, elastically stiff, but at the same time they exhibit high thermal and electrical conductivities and are machineable like graphite. These properties originate from an inherently nanolaminated crystal structure with Mn+1Xn slabs intercalated with pure A-element layers, which also makes them very damage-tolerant [1-2]. Depending on the chosen processing route, MAX phases have been reported to retain their ductility at room temperature, due to their ability to deform by forming kink bands [2]. An appealing property is their resistance to liquid metal corrosion (LMC) even under taxing service conditions of high temperatures and low oxygen concentrations in the liquid metal [3], a fact that makes them good candidate materials for LFRs. Moreover, the appreciable machinability of MAX phases allows the fabrication of geometrically complex components using conventional material removal techniques, such as multi-axial milling. The complex MYRRHA pump impeller geometry makes MAX phases ideal materials for the fabrication of this component.
    Fully-dense MAX phase bulk materials can be made by powder metallurgical processes from elementary powders involving milling, mixing, or mechanical alloying, followed by a thermal treatment usually under pressure-assisted conditions, such as hot-pressing, pulsed electric current sintering (PECS), or hot-isostatic pressing (HIP) [4]. Alternatively, MAX phases can be obtained by thin-film synthesis by means of physical vapor deposition (PVD), chemical vapor deposition (CVD), and solid-state reaction synthesis [5].
    This PhD thesis will address the fabrication and assessment of selected MAX phases and MAX phase-based cermets intended to be used for the fabrication of the MYRRHA pump impeller. The consideration of cermets (i.e., ceramic/metallic material composites) is based on the fact that some of the MAX phase properties (e.g., fracture toughness) might not be sufficient to fully address the MYRRHA pump impeller material requirements.
    Original languageEnglish
    QualificationMaster of Science
    Awarding Institution
    • KU Leuven
    • Vleugels, Jozef, Supervisor, External person
    • Lambrinou, Konstantza, SCK CEN Mentor
    Date of Award20 Jun 2017
    StatePublished - 1 Jul 2017

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